16. carboxylic acids
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Chapter 16 Carboxylic Acids and
Esters
16.1
Carboxylic Acids
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A carboxylic acid
Contains a carboxyl group, which is a carbonyl group(C=O) attached to a hydroxyl group (OH).
Has the carboxyl group on carbon 1.
carbonyl group
O
CH3 COH hydroxyl group or CH3COOH
carboxyl group
Carboxylic Acids
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Models of Carboxylic Acids
The three-dimensional models show the geometryof atoms in carboxylic acid molecules.
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The IUPAC names of carboxylic acids
Replace the -ein the alkane name with -oic acid.
CH4 methane HCOOH methanoic acid
CH3CH3 ethane CH3COOH ethanoic acid
Number substituents from the carboxyl carbon 1.
CH3 O|
CH3CHCH2COH4 3 2 1
3-methylbutanoic acid
IUPAC Names
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The common names of simple carboxylic acids
Are formic acid (1C), acetic acid (2C), propionic acid(3C), and butyric acid (4C).
HCOOH formic acidCH3COOH acetic acid
Locate substituents using , , for the carbonatoms adjacent to the carboxyl carbon.
CH3 | CH3CHCH2COOH
3-methylbutanoic acid (-methylbutryic acid)
Common Names
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Alpha Hydroxy AcidsAlpha hydroxy acids
(AHAs)
Occur naturally in
fruit, milk, andsugarcane.
Are used in skincare products.
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Names and Sources of Some
Carboxylic Acids
TABLE 16.1
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Aromatic Carboxylic Acids
Benzoic acid
Is the aromatic carboxylic acid.
Locates substituents by assigning 1 to the carbonattached to the carboxyl group.
Has common names that assign prefixes ortho,meta, and parafor 2 substituents.
ortho 1, 2 locationmeta 1, 3 location
para 1, 4 location
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Aromatic Carboxylic Acids
OHC
O
OHC
O
OHC
O
Cl
NH2
benzoic acid 3-chlorobenzoic acid 4-aminobenzoic acid
m-chlorobenzoic acid p-aminobenzoic acid
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Give the IUPAC and common names:
A. CH3COOH
CH3|
B. CH3CHCOOH
C.
Learning Check
COOH
Br
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A. CH3COOH ethanoic acid (acetic acid)CH3|
B. CH3CHCOOH 2-methylpropanoic acid(-methylpropionic acid)
C. 2-bromobenzoic acid
(o-bromobenzoic acid)
Solution
COOH
Br
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Preparation of Carboxylic Acids
Carboxylic acids can be prepared by oxidizingprimary alcohols or aldehydes.
The oxidation of ethanol produces ethanoic acid
(acetic acid).
OH O O| [O] || [O] ||
CH3CH2 CH3CH CH3COH
ethanol ethanal ethanoic acid(ethyl alcohol) (acetaldehyde) (acetic acid)
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Learning Check
What alcohol could be used to prepare the following:
1. butanoic acid
2. propanoic acid
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Solution
What alcohol could be used to prepare the following:
[O] [O]
1. butanol butanal butanoic acid
[O] [O]
2. 1-propanol propanal propanoic acid
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16.2Properties of Carboxylic Acids
Chapter 16 Carboxylic Acids and
Esters
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Polarity of Carboxylic AcidsCarboxylic acids
Are strongly polar.
Have two polar groups:
hydroxyl (OH) and carbonyl (C=O).
-
O
+
- +
CH3COH
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Boiling Points of Carboxylic AcidsThe boiling points of carboxylic acids
Are higher than alcohols, ketones, and aldehydes ofsimilar mass.
Are high because they form dimersin whichhydrogen bonds form between the polar groups in thetwo carboxyl groups.
O HO|| |CH3C CCH3
| ||OH O
A dimer of acetic acid
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Comparison of Boiling Points
Compound Molar Mass Boiling Point
O
CH3CH2CH 58 49C
CH3CH2CH2OH 60 97C
O
CH3COH 60 118C
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Solubility in Water
Carboxylic acids
Form hydrogenbonds with many
water molecules.
With 1-4 carbonatoms are very
soluble in water.
Water molecules
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Boiling Points and Solubility
TABLE 16.2
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Acidity of Carboxylic Acids
Carboxylic acids
Are weak acids.
Ionize in water to produce carboxylate ions
and hydronium ions.O O
CH3COH + H2O CH3CO + H3O+
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Neutralization of Carboxylic Acids
Carboxylic acid salts
Are a product of the neutralization of a carboxylic acidwith a strong base.
CH3COOH + NaOH CH3COONa+ + H2O
acetic acid sodium acetate
(carboxylic acid salt)
Areused as preservatives and flavor enhancers.
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Learning Check
Write the equation for the reaction of propanoic acid with
A. water
B. KOH
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Solution
Write the equation for the reaction of propanoic acid with
A. water
CH3CH2COOH + H2O CH3CH2COO + H3O+
B. KOH
CH3CH2COOH + KOH CH3CH2COO K+ + H2O
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Chapter 16 Carboxylic Acids and
Esters
16.3 Esters
16.4 Naming Esters
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Esters
In an ester,
The H in the carboxyl group is replaced
with an alkyl group.
OCH3 COCH3
ester group
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Esterification is
The reaction of a carboxylic acid and alcohol in thepresence of an acid catalyst to produce an ester.
O H+
CH3COH + HOCH2CH3
O
CH3COCH2CH3 + H2Oethyl acetate (an ester)
Esterification
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Write the equation for the reaction of propanoic acidand methanol in the presence of an acid catalyst.
Learning Check
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Write the equation for the reaction of propanoic acid
and methanol in the presence of an acid catalyst.
O
H+CH3CH2COH + HOCH3
propanoic acid methanolO
CH3CH2COCH3 + H2O
Solution
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Naming Esters
The name of an ester contains the names of
The alkyl group from the alcohol.
The carbon chain from the acid withateending.from alcohol from acid
O
methyl
CH3OC CH3ethanoate (acetate)
IUPAC: methylethanoate
common:methyl acetate
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Ester Products
Aspirin
Is used to relieve pain andreduce inflammation.
Is an ester of salicylic acidand acetic acid.
Oil of wintergreen
Is used to soothe sore
muscles. Is an ester of salicylic acid
and methanol.
CH3
O
CO
OH
O
C
OH
CH3O
O
C
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Esters in Plants
Esters giveflowers and
fruits their
pleasantfragrances andflavors.
TABLE 16.4
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Learning Check
Give the IUPAC and common names of the followingcompound, which is responsible for the flavor and odorof pears.
O
CH3COCH2CH2CH3
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Give the IUPAC and common names of the followingcompound, which is responsible for the flavor and odorof pears.
from 1-propanol
O
CH3COCH2CH2CH3
Propyl ethanoate (IUPAC)Propyl acetate (common)
Solution
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Learning Check
Name the following esters:O
A. CH3
CH2
CH2
C
O
CH3
O
B. CH3
CH2
COCH2
CH3
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Solution
A. Methyl butanoate (methyl butyrate)
B. Ethyl propanoate (methyl propionate)
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Learning Check
Write the structure of the following esters:
A. Ethyl pentanoate
B. Propyl butyrate
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Solution
A. Ethyl pentanoateO
CH3CH2CH2CH2COCH2CH3
B. Propyl butyrateO
CH3CH2CH2COCH2CH2CH3
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Chapter 16 Carboxylic Acids and
Esters
16.5
Properties of Esters
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In acid hydrolysis
An ester reacts with water to produce a carboxylicacid and an alcohol.
An acid catalyst is required.O H+
HCOCH2CH3 + H2O
OHCOH +HOCH2CH3
Acid Hydrolysis of Esters
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Base hydrolysis (also called saponification)
Is the reaction of an ester with a strong base.
Produces the salt of the carboxylic acid and analcohol.
O||
CH3COCH2CH3 + NaOHO
CH3CONa+ + HOCH2CH3salt of carboxylic acid alcohol
Base Hydrolysis (Saponification)
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Soaps
The base hydrolysis of long chain fatty acids
produces acid salts called soaps.
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Cleaning Action of Soap
A soap Contains a nonpolar
end that dissolves innonpolar fats and
oils, and a polar endthat dissolves inwater.
Forms groups ofsoap molecules
called micelles thatdissolve in waterand are washedaway.
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Write the organic products when methyl acetate reactswith
A. Water and an acid catalyst
B. KOH
Learning Check
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Write the organic products when methyl acetate reactswith:
A. Water and an acid catalystO
CH3COH + HOCH3
B. KOHO
CH3CO K+ + HOCH3
Solution